friend istream &operator>>

friend istream &operator>> friend istream&operator>>(istream &in,Point &p) ; 还有请问friend istream& operator >>(istream &,zhui &); 里istream是 istream& operator >>(istream &,C &);这句怎样理解? operator friend bool operator>(Triangle,Triangle);头文件里的这句话是什么意思 friend Point operator +(const Point& a,const Point& b); 我是新手 friend A& operator++(A& a)//前++ { a.data += 10; return a; } c++ operator ''operator''是什么意思? keyboard operator 复数 im a keyboard operator.